Plasma cleaning gas and plasma cleaning method

ABSTRACT

The plasma cleaning gas for CVD chamber according to the present invention is a gas for cleaning silicon-containing deposits on the surface of a CVD chamber inner wall and the surfaces of members placed inside the CVD chamber after film forming treatment on a substrate by a plasma CVD apparatus. The cleaning gas comprises 100% by volume of fluorine gas which gas can generate plasma by electric discharge.  
     When 100% by volume of fluorine gas is plasma-generated by electric discharge and then used as a cleaning gas, the extremely excellent etching rate can be attained and further plasma can be stably generated even in the total gas flow rate of 1000 sccm and at a chamber pressure of 400 Pa. Further, the uniformity of cleaning can be also ensured in the above conditions. Additionally the fluorine gas concentration is 100% so that the appatratus is not complicated and thereby the cleaning gas has excellent practicability.

FIELD OF THE INVENTION

[0001] The present invention relates to plasma cleaning gases for CVDchambers, which gases are used in order to remove deposits on the innerwall surface or other surfaces of CVD chambers during film formingtreatment in plasma CVD (Chemical Vapor Deposition) apparatus in whichthe film forming treatment with silicon oxide, silicon nitride etc. isconducted on the substrate surfaces for semiconductors etc., and furtherrelates to processes for plasma cleaning of the CVD chambers.

[0002] More particularly, it relates to plasma cleaning gases for CVDchambers which gases have high uniformity of cleaning deposits on theinner wall, etc. and an excellent etching rate, and relates to processesfor plasma cleaning of the CVD chambers. The term “uniformity ofcleaning” used herein is an indication of stability of generated plasmaand is evaluated in the following manner, as also described in theexamples. A wafer previously deposited with SiO₂ film by CVD is used asa sample and is placed on the lower electrode, and then the etching rateis measured. The evaluation of the uniformity of the etching rate on theinside of the wafer surface is taken as a typical evaluation ofuniformity of cleaning. This property is evaluated likewise hereinafter.

[0003] The term “etching rate” used herein is an indication ofevaluating the rate of cleaning and is evaluated by measuring the rateof etching a SiO₂ thin film on a wafer as described in the examples. Theetching rate is taken as a typical evaluation of cleaning. The propertyis evaluated likewise hereinafter.

BACKGROUND OF THE INVENTION

[0004] Conventionally, in plasma CVD apparatus used in processes ofproducing semiconductors such as LSI, etc., large amounts of perfluorocompounds such as CF₄, C₂F₆, SF₆, NF₃ etc. are used as a cleaning gasfor CVD chambers in order to remove deposits on the surface of the innerwall or other surfaces of the CVD chambers during film formingtreatment. These compounds are stable, and have a very long life in theatmosphere and a high infrared absorption. With regard to global warmingpotential (GWP₁₀₀) of the above perfluoro compounds, on the basis ofcarbon dioxide being 1, CF₄ has 6500, C₂F₆ has 9200, SF₆ has 23900 andNF₃ has 8000 which values are extremely high. Therefore, the compoundshave a high greenhouse effect and affect global warming very greatly.

[0005] Further, in the case of using the perfluoro compounds such asCF₄, C₂F₆, SF₆, NF₃ etc. as a plasma CVD chamber cleaning gas, exhaustgases include the perfluoro compounds themselves which compounds are notdecomposed even if plasma is generated. Further, in the case of usingvarious compounds containing carbon and fluorine such as perfluorocarbon, hydrofluoro carbon (HFC) etc., exhaust gases contain CF₄, etc.which are generated as a by-product. So they induce an environmentalproblem of exhausting global warming gases.

[0006] The gases inviting the greenhouse effect and global warming gascontained in the exhaust gases as described above are hardly absorbed ordecomposed by abatement apparatus (water scrubber) which apparatus hasconventionally been used mainly, so that a decomposition apparatus bychemical reactions including burning with high temperature and highenergy is required.

[0007] Further, in the case that these cleaning gases are used forplasma CVD chambers cleaning, a method that the cleaning gases aregenerated by plasma for cleaning has been attempted for attainingeffective cleaning performance.

[0008] Usually, in plasma cleaning, a proper amount of an additional gassuch as oxygen, argon etc. is mixed with the cleaning gases.

[0009] According to the knowledge of the present inventors, in the mixedgas system of the cleaning gases and the additional gases, withincreasing the concentrations of the cleaning gases in conditions thatthe total gas flow rates are constant, the etching rates tend to beincreased. However, when the cleaning gas concentrations are overconstant concentrations, there are problems such as instability inplasma generation, slowdown or lowering of the etching rate,deterioration in uniformity of cleaning etc. Particularly, using thecleaning gas in a concentration of 100% induces a more marked tendencytoward instability in plasma generation, slowdown or lowering of theetching rate and deterioration in the uniformity of cleaning so that ithas a problem such that it is lacking in practical use.

[0010] On this account, prior to use, the cleaning gases need to bediluted so as to have the peak concentration in the etchingrate-cleaning gas concentration curve or a lower concentration than thepeak concentration. In order to depress the lowering of the etching ratecaused with the dilution, the cleaning condition has been optimized byincreasing the chamber pressure or increasing the gas flow rate incleaning. However, when the chamber pressure is enhanced or the gas flowrate is increased in cleaning, the plasma generation becomes unstable,so that the uniformity of cleaning is deteriorated and efficientcleaning cannot be conducted.

[0011] Of the above cleaning gases, for example, in the use of NF₃, aremote plasma apparatus in which plasma is generated other than aprocess chamber of a CVD apparatus is required for securing a highdecomposition rate which is one of the objects so that the cleaningefficiency is improved, contamination of undecomposed NF₃ into exhaustgases is avoided. However, the CVD apparatus provided with the remoteplasma apparatus has a problem in that the apparatus is complicated andthereby the production cost is high.

[0012] Further, in conventionally used cleaning gases, when the chamberpressure is enhanced or the gas flow rate is increased, thedecomposition rate of the cleaning gases in plasma and the plasmastability (uniformity of cleaning) are remarkably decreased so that thecleaning gases themselves are contained in the exhaust gases resultingin increasing the emission amount of global warming substances.Therefore, it is necessary to take measures for abatement of the gases.

[0013] Accordingly, plasma cleaning gases which are used for chambercleaning after the CVD process in producing semiconductors such as LSI,etc., and have a low greenhouse effect and a low global warmingpotential, excellent uniformity of cleaning even in diluting conditionsor not, and also have an effective etching rate, and a process forplasma cleaning has been desired.

[0014] In the light of the foregoing, the present inventors haveearnestly studied for solving the above problems, and found that when amixed gas of fluorine gas and a gas incapable of substantially reactingwith fluorine in plasma is used, plasma can be generated stably withouta remote plasma apparatus in wider conditions than the use of, forexample, NF₃ and further the excellent etching rate can be providedwithout lowering of the etching rate. The present inventors furtherfound that for example, as will be described in Examples 34 and 37, andComparative Examples 30 and 31 of the present specification, in the casethat the total gas flow rate is 1000 sccm, when the chamber pressurecondition is changed from 250 Pa to a higher pressure of 400 Pa, in theuse of a mixed gas containing 20% by volume of NF₃, the uniformity ofcleaning is decreased, but in the use of a mixed gas containing the same20% by volume of fluorine gas, the proper uniformity of cleaning can besecured.

[0015] Further, the present inventors found that when 100% by volume offluorine gas is generated by plasma and then is used as a cleaning gas,the extremely excellent etching rate can be attained without the use ofa remote plasma apparatus, and also even in conditions that the totalgas flow rate is about 1000 sccm and the chamber pressure is about 400Pa, plasma can stably be generated and the proper uniformity of cleaningcan be secured.

[0016] Thus, the present invention has been accomplished.

[0017] The present invention is intended to solve the problemsassociated with the prior arts as described above, it is an object ofthe present invention to provide a plasma cleaning gas for CVD chamberswhich gas has excellent uniformity of cleaning and an effective etchingrate in cleaning in the conditions that the total gas flow rate is about1000 sccm and the chamber pressure is about 400 Pa under the dilutioncondition or under no dilution condition. It is a further object of theinvention to provide a process for plasma cleaning CVD chambers.

DISCLOSURE OF THE INVENTION

[0018] The first plasma cleaning gas for CVD chambers according to thepresent invention comprises 100% by volume of fluorine gas capable ofgenerating plasma by electric discharge and is used for cleaningsilicon-containing deposits on the surface of a CVD chamber inner walland the surfaces of members placed inside the CVD chamber after filmforming treatment on a substrate by a plasma CVD apparatus.

[0019] The first process of plasma cleaning for CVD chambers accordingto the present invention comprises cleaning silicon-containing depositson the surface of a CVD chamber inner wall and the surfaces of membersplaced inside the CVD chamber by plasma generated from 100% by volume offluorine gas by electric discharge, after film forming treatment on asubstrate in a plasma CVD apparatus.

[0020] The silicon-containing deposits preferably comprise at least oneselected from:

[0021] (1) silicon,

[0022] (2) a compound comprising silicon and at least one of oxygen,nitrogen, fluorine and carbon, and

[0023] (3) a compound of a high melting point-having metal silicide.

[0024] The chamber pressure in the plasma CVD apparatus is preferablyfrom 50 Pa to 1000 Pa, and the flow rate of fluorine gas introducinginto a plasma generating part is preferably from 50 sccm to 1000 sccm inthe cleaning.

[0025] The plasma generation from the above-described fluorine gas ispreferably conducted by electric discharge in a process chamber of theplasma CVD apparatus whereinto fluorine gas has been introduced.

[0026] The second plasma cleaning gas for CVD chambers according to thepresent invention comprises fluorine gas capable of generating plasma byelectric discharge and a gas substantially incapable of reacting withfluorine in plasma, and is used for cleaning silicon-containing depositson the surface of a CVD chamber inner wall and the surfaces of membersplaced inside the CVD chamber after film forming treatment on asubstrate by a plasma CVD apparatus.

[0027] It is preferred that the concentration of the fluorine gascapable of generating plasma by electric discharge be more than 20% byvolume to less than 100% by volume and the concentration of the gassubstantially incapable of reacting with fluorine in plasma be more than0% by volume to not more than 80% by volume provided that the totalconcentration of the fluorine gas capable of generating plasma byelectric discharge and the gas substantially incapable of reacting withfluorine is 100% by volume.

[0028] Further, it is more preferred that the concentration of thefluorine gas capable of generating plasma by electric discharge be morethan 30% by volume to less than 100% by volume and the concentration ofthe gas substantially incapable of reacting with fluorine in plasma bemore than 0% by volume to not more than 70% by volume provided that thetotal concentration of the fluorine gas capable of generating plasma byelectric discharge and the gas substantially incapable of reacting withfluorine in plasma is 100% by volume.

[0029] The gas substantially incapable of reacting with fluorine inplasma is preferably at least one selected from the group of nitrogen,oxygen, carbon dioxide, N₂O, dried air, argon, helium and neon.

[0030] The second process of plasma cleaning for CVD chambers accordingto the present invention comprises cleaning silicon-containing depositson the surface of a CVD chamber inner wall and the surfaces of membersplaced inside the CVD chamber using a cleaning gas for plasma CVDchambers comprising fluorine gas capable of generating plasma byelectric discharge and a gas substantially incapable of reacting withfluorine in plasma after film forming treatment on a substrate by meansof a plasma CVD apparatus.

[0031] It is preferred that the concentration of the fluorine gascapable of generating plasma by electric discharge be more than 20% byvolume to less than 100% by volume and the concentration of the gassubstantially incapable of reacting with fluorine in plasma be more than0% by volume to not more than 80% by volume provided that the totalconcentration of the fluorine gas capable of generating plasma byelectric discharge and the gas substantially incapable of reacting withfluorine is 100% by volume.

[0032] The pressure in the chamber is preferably from 50 Pa to 1000 Pa,and the flow rate of fluorine gas is preferably from 50 sccm to 1000sccm in the cleaning.

[0033] The plasma generation from fluorine gas is preferably conductedby electric discharge in a process chamber of the plasma CVD apparatuswhereinto fluorine gas has been introduced.

BRIEF DESCRIPTION OF THE DRAWING

[0034]FIG. 1 is a graph showing a relation between a gas concentrationand an etching rate concerning the results of Examples 1 to 17 andComparative Examples 1 to 13.

PREFERRED EMBODIMENTS OF THE INVENTION

[0035] The present invention will be described in detail hereinafter.

[0036] (Plasma Cleaning Gas for CVD Chambers and Process of PlasmaCleaning According to the First Invention)

[0037] The plasma cleaning gas for CVD chambers according to the firstinvention is used for cleaning silicon-containing deposits on thesurface of a CVD chamber inner wall and the surfaces of members placedinside the CVD chamber after film forming treatment on a substrate by aplasma CVD apparatus. The cleaning gas comprises 100% by volume offluorine gas and generates plasma from fluorine gas by electricdischarge to remove the silicon-containing deposits as described above.

[0038] The first process of plasma cleaning for CVD chambers accordingto the invention comprises cleaning, by plasma generated from 100% byvolume of fluorine gas by electric discharge, silicon-containingdeposits on the surface of a CVD chamber inner wall and the surfaces ofmembers placed inside the CVD chamber after film forming treatment on asubstrate by means of a plasma CVD apparatus.

[0039] The term “plasma cleaning for CVD chambers” used in the presentspecification means removing deposits on the surface of a chamber innerwall and the surfaces of members such as jigs, piping or other insidecomponents placed in semiconductor producing apparatus, for example, CVDapparatus or the like after the CVD process in a production process ofsemiconductors such as LSI, etc.

[0040] Further, the term “plasma generation” used in the presentspecification means that plasma is generated by introducing fluorine gasor the mixed gas of fluorine gas and the gas substantially incapable ofreacting with fluorine in plasma and electrically discharging at aplasma generating part (CVD chamber or remote plasma apparatus).

[0041] The targeted compound of the CVD chamber cleaning with such 100%by volume of fluorine gas may include the above describedsilicon-containing deposits on the surfaces of the inner wall of CVDchambers and jigs or the like of CVD apparatus in the CVD method, etc.The silicon-containing deposits comprise, for example, at least oneselected from:

[0042] (1) silicon,

[0043] (2) a compound comprising silicon and at least one of oxygen,nitrogen, fluorine and carbon, and

[0044] (3) a compound of a high melting point-having metal silicide.Specific examples thereof are Si, SiO₂, Si₃N₄, and high meltingpoint-having metal silicides such as WSi.

[0045] In the process of plasma cleaning for CVD chambers according tothe invention, the plasma generation from fluorine gas by electricdischarge may be conducted in a remote chamber or in a process chamberof a plasma CVD apparatus whereinto fluorine gas is introduced withoutusing the remote chamber.

[0046] Of these, it is desired to generate plasma from fluorine gas inthe process chamber of the plasma CVD apparatus.

[0047] When plasma is generated from fluorine gas in the processchamber, the cleaning treatment of deposits in the CVD chamber can beconducted efficiently for a short time, and also plasma can be stablygenerated. Further, the apparatus can be compacted so that it ispractical as compared with the plasma generation in the remote chamber.

[0048] The first cleaning gas of the invention comprises 100% by volumeof fluorine gas and is used for plasma cleaning for CVD chambers.Usually, in the case that C₂F₆ or NF₃ is used as a cleaning gas, 100% byvolume of the gas is not used, and it is necessary to mix the gas with adiluting gas such as oxygen, argon, nitrogen etc. for use. Depending tothe conditions, in the case of C₂F₆ or NF₃, when the C₂F₆ or NF₃concentration in the cleaning gas is more than about 20 to 40% byvolume, the rise of the etching rate based on the concentration in thecleaning gas, in a constant total gas flow rate, is slowed down and theetching rate is lowered finally. In the case that the total gas flowrate is 1000 sccm and the chamber pressure is about 400 Pa as describedabove, these gases cannot generate plasma stably. When the gasconcentration or the chamber pressure is increased, the uniformity ofcleaning becomes worse.

[0049] However, in the plasma cleaning gas and the process of plasmacleaning for CVD chambers according to the first or second invention,fluorine gas is used and the cleaning gas has a specific characteristicsuch that the etching rate is increased almost linearly with theincrease of the concentration of fluorine gas in the condition that thetotal gas flow rate is constant. Even if the cleaning gas comprises 100%by volume of fluorine gas, the extremely excellent etching rate can beattained and also the uniformity of cleaning is extremely excellent.

[0050] When 100% by volume of fluorine gas is used, plasma can be stablygenerated, not only in the case that the chamber pressure is 150 Pa(flow rate 150 sccm) but also in the case that the chamber pressure is250 Pa (flow rate 300 sccm). The cleaning gas having the specificcharacteristic as above has not been found out previously so long as thepresent inventors have investigated.

[0051] When the cleaning is conducted with the plasma cleaning gasaccording to the first invention, the chamber pressure is preferablyfrom 50 Pa to 1000 Pa, more preferably from 150 Pa to 1000 Pa. Thefluorine gas flow rate is preferably from 50 sccm to 1000 sccm, morepreferably 150 to 1000 sccm.

[0052] When the chamber pressure and the fluorine gas flow rate are inthe above ranges, the excellent etching rate can be attained, and thestabilization of plasma generation and the uniformity of cleaning can bekept excellent.

[0053] The chamber pressure is an inner pressure of a process chamber ina CVD apparatus and, in general, is automatically regulated by setting.

[0054] (Plasma Cleaning Gas for CVD Chambers and Process of PlasmaCleaning According to the Second Invention)

[0055] The plasma cleaning gas for CVD chambers according to the secondinvention is used for cleaning silicon-containing deposits on thesurface of a CVD chamber inner wall and the surfaces of members placedinside the CVD chamber after film forming treatment on a substrate by aplasma CVD apparatus. The plasma cleaning gas comprises fluorine gascapable of generating plasma by electric discharge and a gassubstantially incapable of reacting with fluorine in plasma.

[0056] The second process of plasma cleaning for CVD chambers accordingto the invention comprises cleaning silicon-containing deposits on thesurface of a CVD chamber inner wall and the surfaces of members placedinside the CVD chamber by plasma generated from fluorine gas by electricdischarge using the plasma cleaning gas for CVD chambers composed offluorine gas capable of generating plasma by electric discharge and thegas substantially incapable of reacting with fluorine in plasma, afterfilm forming treatment on a substrate by means of a plasma CVDapparatus.

[0057] In the present specification, “fluorine” contained in the gassubstantially incapable of reacting with fluorine includes fluorinemolecules, fluorine atoms, fluorine radicals, fluorine ions etc.

[0058] The concentration of the fluorine gas capable of generatingplasma by electric discharge is preferably more than 20% by volume toless than 100% by volume, and the concentration of the gas substantiallyincapable of reacting with fluorine in plasma is preferably more than 0%by volume to not less than 80% by volume. The sum of the concentrationof the fluorine gas capable of generating plasma by electric dischargeand the concentration of the gas substantially incapable of reactingwith fluorine in plasma is 100% by volume.

[0059] The concentration of the fluorine gas capable of generatingplasma by electric discharge is, further, preferably more than 30% byvolume to less than 100% by volume, more preferably not less than 40% byvolume to less than 100% by volume, and especially not less than 70% byvolume to less than 100% by volume, and the concentration of the gassubstantially incapable of reacting with fluorine in plasma is, further,preferably more than 0% by volume to not more than 70% by volume, morepreferably more than 0% by volume to less than 60% by volume, andespecially more than 0% by volume to less than 30% by volume.

[0060] When the fluorine gas concentration is in the above range, theexcellent etching rate can be attained and the uniformity of cleaning isgood even in the conditions that the total gas flow rate is about 1000sccm and the chamber pressure is about 400 Pa. Further, plasma can begenerated stably in the presence of fluorine gas.

[0061] As described above, the etching rate has a specificcharacteristic such that the etching rate and the concentration offluorine gas are increased almost linearly so that the etching rate iseasily predictable from the fluorine gas concentration and it iseffective in practical use.

[0062] In the case when fluorine gas concentration is limited to be notmore than 50% by volume in transportation, etc., the concentration offluorine gas for submitting to plasma treatment is preferably more than20% by volume, more preferably more than 30% by volume. Particularly, itis preferably not more than 50% by volume, so that the cleaning gas hasa practicability maintainable etching rate and also, as a cleaning gas,excellent transportation property and storage stability, and simplehandling. Furthermore, as described above, although this concentrationrange is a relatively low concentration range, the uniformity ofcleaning is not deteriorated even if the chamber pressure is increasedin order to increase the etching rate in this concentration range.

[0063] Further, even if the concentration of fluorine gas for submittingto plasma treatment is in a low range of 5 to 20% by volume, theuniformity of cleaning is not deteriorated by increasing the chamberpressure in order to increase the etching rate.

[0064] The gas substantially incapable of reacting with fluorine inplasma is preferably at least one selected from the group of nitrogen,oxygen, carbon dioxide, N₂O, dried air, argon, helium and neon. Amongthem, it is more preferably at least one selected from the group ofoxygen, carbon dioxide and dried air.

[0065] The fluorine gas introduced in plasma generates fluorineradicals. Using the gas substantially incapable of reacting with thefluorine radicals, fluorine molecules, fluorine ions etc., theby-product generation can be depressed and the cleaning can be conductedefficiently.

[0066] Further, using oxygen, carbon dioxide and dried air, fluorineradicals can be generated stably at low cost.

[0067] When the cleaning is conducted using the plasma cleaning gasaccording to the second invention, the chamber pressure is preferablyfrom 50 Pa to 1000 Pa, more preferably 150 Pa to 1000 Pa. The fluorinegas flow rate is preferably from 50 sccm to 1000 sccm, more preferably150 sccm to 1000 sccm.

[0068] When the chamber pressure and the fluorine gas flow rate are inthe above ranges, the excellent etching rate can be attained and alsothe stabilization of plasma generation and the uniformity of cleaningcan be kept excellent.

[0069] In the case of using the plasma cleaning gas for CVD chambersaccording to the second invention, the plasma generation from fluorinegas by electric discharge may be conducted in a remote chamber or byintroducing fluorine gas into a plasma CVD apparatus and generatingplasma from fluorine gas in a process chamber of the CVD apparatus,without using the remote chamber.

[0070] Of these, it is desirable to generate plasma from fluorine gas inthe process chamber of the plasma CVD apparatus.

[0071] When plasma is generated from fluorine gas in the processchamber, the cleaning treatment of deposits in the CVD chamber can beconducted efficiently for a short time, and also plasma can be stablygenerated similar to the first invention. Further, the apparatus can becompacted so that it is practical as compared with the plasma generationin the remote chamber.

EXAMPLES

[0072] The present invention will be described in more detail withreference to the following non-limiting examples hereinafter.

[0073] In the present examples, as one of the properties of the cleaninggas, the cleaning rate for deposits, which should be removed wasunequivocally evaluated by the etching rate of a SiO₂ thin film on awafer.

[0074] The method of measuring the etching rates of fluorine gas anddiluted fluorine gas is shown below. A Si wafer previously depositedSiO₂ film thereon having a thickness of about 11000 Å by the plasma CVDmethod was used as a sample and a parallel plate plasma enhanced CVDapparatus was used. In the conditions as described in Examples, thewafer as a sample was placed on a lower electrode of the parallel plateelectrodes and etched. The etching rate was determined by accuratelymeasuring the film thickness on nine fixed points of the sample beforeand after the etching with a spectroscopic reflectmeter film thicknessmeasuring instrument and measuring the decrease in the film thickness.

[0075] The uniformity of cleaning was determined from the maximum valueand the minimum value of the etching rates on the nine fixed points withthe following formula.

[maximum value−minimum value)/(maximum value+minimum value)]×100(%)

Examples 1 to 17 and Comparative Examples 1 to 16

[0076] The dependency of the etching rate on the gas kind and the gasconcentration was examined using F2, C₂F₆ and NF₃ as a cleaning gas andthe gases shown in the tables as a dilution gas in the followingconditions. The results are shown in Tables 1 to 7. Further, the resultsare shown in FIG. 1. Total gas flow rate: 300 sccm Chamber pressure: 250Pa Electrode temperature: 300° C. RF electric power: 750 W Distancebetween electrodes: 50 mm Electric discharge time: 30 sec

[0077] TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Cleaning gas composition F₂amount (mol %) 10 25 50 75 100 O_(2 amount (mol %)) 90 75 50 25 0 Aramount (mol %) — — — — — N₂ amount — — — — — (mol %) Total gas amount100 100 100 100 100 (mol %) Etching rate (Å/min) 3460 8190 15960 2180029420 Uniformity of cleaning 3 3.2 4 3.9 4.1 (%)

[0078] TABLE 2 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Cleaning gascomposition F₂ amount 5 10 20 25 50 75 (mol %) O₂ amount — — — — — —(mol %) Ar amount 95 90 80 75 50 25 (mol %) N₂ amount — — — — — — (mol%) Total gas 100 100 100 100 100 100 amount (mol %) Etching rate 21904230 7090 8800 16440 22240 (Å/min) Uniformity of 4.2 3.6 3.3 3.9 3.4 4.5cleaning (%)

[0079] TABLE 3 Ex. 12 Ex. 13 Ex. 14 Cleaning gas composition F₂ amount(mol %) 25 50 75 O₂ amount (mol %) — — — Ar amount (mol %) — — — N₂amount mol % 75 50 25 Total gas amount (mol %) 100 100 100 Etching rate(Å/min) 8570 16230 22450 Uniformity of cleaning (%) 3.2 6.2 4.2

[0080] TABLE 4 Dried air Ex. 15 Ex. 16 Ex. 17 Cleaning gas compositionF₂ amount (mol %) 25 50 75 O₂ amount (mol %) 15 10 5 Ar amount (mol %) —— — N₂ amount (mol %) 60 40 20 Total gas amount (mol %) 100 100 100Etching rate (Å/min) 8490 16180 22320 Uniformity of cleaning (%) 3.2 4.34

[0081] TABLE 5 Comparative Example 1 2 3 4 5 6 7 C₂F₆ amount (mol %) 2040 45 50 55 60 70 O₂ amount (mol %) 80 60 55 50 45 40 30 NF₃ amount (mol%) — — — — — — — Ar amount (mol %) — — — — — — — Total gas amount (mol%) 100 100 100 100 100 100 100 Etching rate (Å/min) 7810 11810 1227012410 12140 11140 7590 Uniformity of cleaning (%) 4.7 4.3 4 3.5 4 3.11.9

[0082] TABLE 6 Comparative Example 8 9 10 11 12 13 Cleaning gascomposition C₂F₆ amount — — — — — — (mol %) O₂ amount — — — — — — (mol%) NF₃ amount 10 20 30 40 50 60 (mol %) Ar amount 90 80 70 60 50 40 (mol%) Total gas 100 100 100 100 100 100 amount (mol %) Etching rate 50709080 12510 15310 17180 16080 (Å/min) Uniformity of 3.3 3.4 3.4 4.1 24 36cleaning (%)

[0083] TABLE 7 Comparative Example 14 15 16 Cleaning gas compositionC₂F₆ amount (mol %) — — — O₂ amount (mol %) — — — NF₃ amount (mol %) 1030 40 N₂ amount (mol %) 90 70 60 Total gas amount (mol %) 100 100 100Etching rate (Å/min) 4872 12298 14316 Uniformity of cleaning (%) 3.2 5.431.5

[0084] As is clear from the results, fluorine gas in any concentrationuntil 100% had almost no influence on the uniformity of etchingindependent on the kind of the added gas.

[0085] On the contrary, with respect to C₂F₆, in a high C₂F₆concentration, the uniformity of cleaning was not deteriorated, however,the etching rate was largely lowered.

[0086] With regard to NF₃, in the case that the added gas was argon,when the NF₃ concentration was not less than 50%, the uniformity ofcleaning was largely deteriorated and when the NF₃ concentration was60%, the lowering of the etching rate was observed. In the case that theadded gas was nitrogen, when the NF₃ concentration was 40%, theuniformity of cleaning was largely deteriorated. It is presumed that thedeterioration shows an indication such that plasma generated is biasedand thereby plasma is not generated stably.

Examples 18 to 37

[0087] The dependency of the etching rate on the gas flow rate and thechamber pressure was examined by using F₂ as a cleaning gas and Ar as adilution gas in a low F₂ concentration of 5 to 20% by volume in theconditions as shown in Tables 8 to 11. The results are shown in Tables 8to 11. Electrode temperature: 300° C. RF electric power: 750 W Distancebetween electrodes: 50 mm Electric discharge time: 30 sec

[0088] TABLE 8 Ex 18 Ex 19 Ex 20 Ex. 21 Total gas flow rate (sccm) 300300 300 300 Chamber pressure (Pa) 250 250 250 150 Cleaning gascomposition F₂ amount (mol %) 5 10 20 5 Ar amount (mol %) 95 90 80 95Total gas amount (mol %) 100 100 100 100 Etching rate (Å/min) 2192 42347089 2731 Uniformity of cleaning (%) 4.2 3.6 3.3 2.9

[0089] TABLE 9 Ex 22 Ex 23 Ex 24 Ex 25 Ex 26 Total gas flow rate 500 500500 500 500 (sccm) Chamber pressure (Pa) 250 250 250 150 400 Cleaninggas composition F₂ amount (mol %) 5 10 20 5 5 Ar amount (mol %) 95 90 8095 95 Total gas amount (mol 100 100 100 100 100 %) Etching rate (Å/min)2543 4801 8473 3324 6297 Uniformity of cleaning 3.8 3.4 3.5 2.6 2.6 (%)

[0090] TABLE 10 Ex 27 Ex 28 Ex 29 Ex 30 Ex 31 Total gas flow rate 700700 700 700 700 (sccm) Chamber pressure (Pa) 250 250 250 150 400Cleaning gas composition F₂ amount (mol %) 5 10 20 5 5 Ar amount (mol %)95 90 80 95 95 Total gas amount (mol 100 100 100 100 100 %) Etching rate(Å/min) 2777 5241 9114 3308 6923 Uniformity of cleaning 3.7 3.2 3.4 2.35.3 (%)

[0091] TABLE 11 Example 32 33 34 35 36 37 Total gas flow 1000 1000 10001000 1000 1000 rate (sccm) Chamber 250 250 250 150 400 400 pressure (Pa)Cleaning gas composition F₂ amount 5 10 20 5 5 20 (mol %) Ar amount 9590 80 95 95 80 (mol %) Total gas 100 100 100 100 100 100 amount (mol %)Etching rate 2978 5519 9893 3531 7800 13552 (Å/min) Uniformity of 3.63.3 3.4 2.3 5.3 4.8 cleaning (%)

[0092] As is clear from the results, in the case that the cleaning gashaving a F2 concentration of 5 to 20% was used, even if the flow ratewas increased in the experimental range or the pressure is increased,the uniformity of cleaning proved to be excellent.

Examples 38 to 55

[0093] The dependency of the etching rate on the gas flow rate and thechamber pressure was examined by using a cleaning gas having a F₂concentration of 100% by volume in the conditions as shown in Tables 12to 16. The results are shown in Tables 12 to 16. Electrode temperature:300° C. RF electric power: 750 W Distance between electrodes: 50 mmElectric discharge time: 30 sec

[0094] TABLE 12 Example 38 39 Total gas flow rate (sccm) 100 100 Chamberpressure (Pa) 50 80 Cleaning gas composition 100 100 F₂ amount (mol %)Total gas amount (mol %) 100 100 Etching rate (Å/min) 5119 8239Uniformity of cleaning (%) 1.6 1.5

[0095] TABLE 13 Example 40 41 42 Total gas flow rate (sccm) 150 150 150Chamber pressure (Pa) 50 80 100 Cleaning gas composition 100 100 100 F₂amount (mol %) Total gas amount (mol %) 100 100 100 Etching rate (Å/min)4664 8981 10939 Uniformity of cleaning (%) 1.6 0.6 2.4

[0096] TABLE 14 Example 43 44 45 46 Total as flow rate (sccm) 200 200200 200 Chamber pressure (Pa) 50 80 100 150 Cleaning gas composition 100100 100 100 F₂ amount (mol %) Total gas amount (mol %) 100 100 100 100Etching rate (Å/min) 5144 8270 11173 17812 Uniformity of cleaning (%)1.4 1.7 2.5 2.7

[0097] TABLE 15 Example 47 48 49 50 Total gas flow rate (sccm) 250 250250 250 Chamber pressure (Pa) 50 80 100 200 Cleaning gas composition 100100 100 100 F₂ amount (mol %) Total gas amount (mol %) 100 100 100 100Etching rate (Å/min) 4468 8733 12406 23590 Uniformity of cleaning (%) 21.2 1.9 3

[0098] TABLE 16 Example 51 52 53 54 55 Total gas flow rate 300 300 300300 300 (sccm) Chamber pressure (Pa) 50 80 100 150 250 Cleaning gas 100100 100 100 100 composition F₂ amount (mol %) Total gas amount 100 100100 100 100 (mol %) Etching rate (Å/min) 5012 9235 10927 18484 29416Uniformity of cleaning 1.5 1.3 2.1 2.6 4.1 (%)

[0099] As is clear from the results, in an F₂ concentration of 100%,even if the flow rate was increased in the experimental range, or thepressure is increased, the uniformity of cleaning proved to beexcellent.

Comparative Examples 17 to 29 and Comparative Examples 8 to 13 (ShownAgain)

[0100] With regard to the etching rate and the uniformity of cleaning,the dependency of NF₃ on the concentration and the chamber pressure wasexamined using NF₃ as a cleaning gas and Ar as a dilution gas in theconditions as shown in Tables 17 to 20. The results are shown in Tables17 to 20. Total gas flow rate: 300 sccm Electrode temperature: 300° C.RF electric power: 750 W Distance between electrodes: 50 mm Electricdischarge time: 30 sec

[0101] TABLE 17 Comparative Example 17 18 19 20 21 Chamber pressure (Pa)100 100 100 100 100 Cleaning gas composition NF₃ amount (mol %) 40 50 8090 100 Ar amount (mol %) 60 50 20 10 0 Total gas amount 100 100 100 100100 (mol %) Etching rate (Å/min) 8430 10198 12170 13082 13390 Uniformityof cleaning 0.8 1.6 4.1 14.2 24.8 (%)

[0102] TABLE 18 Comparative Example 22 23 24 25 Chamber pressure (Pa)150 150 150 150 Cleaning gas composition NF₃ amount (mol %) 60 70 80 90Ar amount (mol %) 40 30 20 10 Total gas amount (mol %) 100 100 100 100Etching rate (Å/min) 12594 13779 13574 14389 Uniformity of cleaning (%)5.7 21.1 34.6 40.9

[0103] TABLE 19 Comparative Example 26 27 28 29 Chamber pressure (Pa)200 200 200 200 Cleaning gas composition NF₃ amount (mol %) 40 50 60 70Ar amount (mol %) 60 50 40 30 Total gas amount (mol %) 100 100 100 100Etching rate (Å/min) 12308 14366 15214 14987 Uniformity of cleaning (%)3.4 8.2 28.4 38.2

[0104] TABLE 20 Comparative Example 8 9 10 11 12 13 Chamber 250 250 250250 250 250 pressure (Pa) Cleaning gas composition NF₃ amount 10 20 3040 50 60 (mol %) Ar amount 90 80 70 60 50 40 (mol %) Total gas 100 100100 100 100 100 amount (mol %) Etching rate 5070 9080 12510 15310 1718016080 (Å/min) Uniformity of 3.3 3.4 3.4 4.1 24 36 cleaning (%)

[0105] As is clear from the results, in the case that NF₃ was used as acleaning gas, the uniformity of cleaning was largely deteriorated withthe increase of the NF₃ concentration. Further, the uniformity ofcleaning was largely deteriorated with the increase of the chamberpressure.

Examples 34 and 37 (Shown Again) and Comparative Examples 30 and 31

[0106] The dependency of the etching rate and that of the uniformity ofcleaning on the chamber pressure were examined by using F₂ or NF₃ as acleaning gas and Ar as a dilution gas in a concentration of F₂ or NF₃ of20% by volume in the conditions as shown in Tables 21 and 22. Theresults are shown in Tables 21 and 20. Total gas flow rate: 1000 sccmElectrode temperature: 300° C. RF electric power: 750 W Distance betweenelectrodes: 50 mm Electric discharge time: 30 sec

[0107] TABLE 21 Ex 34 Ex 37 Total gas flow rate (sccm) 1000 1000 Chamberpressure (Pa) 250 400 Cleaning gas composition F₂ amount (mol %) 20 20Ar amount (mol %) 80 80 Total gas amount (mol %) 100 100 Etching rate(Å/min) 9893 13552 Uniformity of cleaning (%) 3.4 4.8

[0108] TABLE 22 Comparative Ex 30 Ex 31 Total gas flow rate (sccm) 10001000 Chamber pressure (Pa) 250 400 Cleaning gas composition NF₃ amount(mol %) 20 20 Ar amount (mol %) 80 80 Total gas amount (mol %) 100 100Etching rate (Å/min) 12260 15380 Uniformity of cleaning (%) 3.7 19.2

[0109] As is clear from the results, in the case that the total gas flowrate is 1000 sccm, when the chamber pressure was changed from 250 Pa toa higher pressure of 400 Pa, the uniformity of cleaning was deterioratedin the use of 20% by volume of NF₃, but the good uniformity of cleaningis ensured in the use of 20% by volume of fluorine gas.

INDUSTRIAL APPLICABILITY

[0110] In the present invention, because fluorine gas is used as acleaning gas, silicon-containing deposits after CVD process can becleaned at a high rate without using CF₄, C₂F₆, SF₆, NF₃ etc. which havea high global warming potential, and exhaust gas can be treated withconventional water scrubber. Therefore, the cleaning can be accomplishedwith exhausting a slight amount of exhaust gases having the greenhouseeffect and the global warming effect.

[0111] Further, using the mixed gas of fluorine gas and the gasincapable of substantially reacting with fluorine in plasma in specificamounts, plasma can stably be generated even in the conditions that thetotal gas flow rate is about 1000 sccm and the chamber pressure is about400 Pa. Additionally, the etching rate is not lowered and the excellentetching rate can be provided. Further, for example, even if the mixedgas has a low concentration of fluorine gas of 5 to 20% by volume, theuniformity of cleaning can be ensured even in the conditions that thetotal gas flow rate and the chamber pressure are as described above.Further, the mixed gas having a low concentration of fluorine gas issimple in handleability.

[0112] Furthermore, when plasma is generated from 100% by volume offluorine gas by electric discharge and submitted to use as a cleaninggas, the extremely excellent etching rate can be attained, and plasmacan stably be generated even in high-pressure conditions and also theuniformity of cleaning can be ensured even in high-pressure conditions.Additionally, the cleaning gas has a fluorine gas concentration of 100%so that the device is not complicated and the cleaning gas is excellentin practicability.

What is claimed is:
 1. A plasma cleaning gas for CVD chambers which gascomprises 100% by volume of fluorine gas capable of generating plasma byelectric discharge and is used for cleaning silicon-containing depositson the surface of a CVD chamber inner wall and the surfaces of membersplaced inside the CVD chamber after film forming treatment on asubstrate by means of a plasma CVD apparatus.
 2. The plasma cleaning gasfor CVD chambers according to claim 1 wherein the silicon-containingdeposits comprise at least one selected from: (1) silicon, (2) acompound comprising silicon and at least one of oxygen, nitrogen,fluorine and carbon, and (3) a compound of a high melting point-havingmetal silicide.
 3. A process of plasma cleaning for CVD chambers whichprocess comprises cleaning silicon-containing deposits on the surface ofa CVD chamber inner wall and the surfaces of members placed inside theCVD chamber by plasma generated from 100% by volume of fluorine gas byelectric discharge, after film forming treatment on a substrate by meansof a plasma CVD apparatus.
 4. The process of plasma cleaning for CVDchambers according to claim 3 wherein the silicon-containing depositscomprise at least one selected from: (1) silicon, (2) a compoundcomprising silicon and at least one of oxygen, nitrogen, fluorine andcarbon, and (3) a compound of a high melting point-having metalsilicide.
 5. The process of plasma cleaning for CVD chambers accordingto claim 3 or 4 wherein the chamber pressure in the plasma CVD apparatusis from 50 Pa to 1000 Pa, and the flow rate of fluorine gas introducinginto a plasma generating part is from 50 sccm to 1000 sccm in thecleaning.
 6. The process of plasma cleaning for CVD chambers accordingto any one of claims 3 to 5 wherein the plasma generation from fluorinegas is conducted by electric discharge in a process chamber of theplasma CVD apparatus whereinto fluorine gas has been introduced.
 7. Aplasma cleaning gas for CVD chambers which gas comprises fluorine gascapable of generating plasma by electric discharge and a gassubstantially incapable of reacting with fluorine in plasma, and is usedfor cleaning silicon-containing deposits on the surface of a CVD chamberinner wall and the surfaces of members placed inside the CVD chamberafter film forming treatment on a substrate by a plasma CVD apparatus.8. The plasma cleaning gas for CVD chambers according to claim 7 whereinthe concentration of the fluorine gas capable of generating plasma byelectric discharge is more than 20% by volume to less than 100% byvolume and the concentration of the gas substantially incapable ofreacting with fluorine in plasma is more than 0% by volume to not morethan 80% by volume provided that the total concentration of the fluorinegas capable of generating plasma by electric discharge and the gassubstantially incapable of reacting with fluorine is 100% by volume. 9.The plasma cleaning gas for CVD chambers according to claim 7 whereinthe concentration of the fluorine gas capable of generating plasma byelectric discharge is more than 30% by volume to less than 100% byvolume and the concentration of the gas substantially incapable ofreacting with fluorine in plasma is more than 0% by volume to not morethan 70% by volume provided that the total concentration of the fluorinegas capable of generating plasma by electric discharge and the gassubstantially incapable of reacting with fluorine is 100% by volume. 10.The plasma cleaning gas for CVD chambers according to any one of claims7 to 9 wherein the gas substantially incapable of reacting with fluorinein plasma is at least one selected from the group of nitrogen, oxygen,carbon dioxide, N₂O, dried air, argon, helium and neon.
 11. A process ofplasma cleaning for CVD chambers which process comprises cleaningsilicon-containing deposits on the surface of a CVD chamber inner walland the surfaces of members placed inside the CVD chamber by plasmagenerated from fluorine gas by electric discharge using a plasmacleaning gas for CVD chambers comprising fluorine gas capable ofgenerating plasma by electric discharge and a gas substantiallyincapable of reacting with fluorine in plasma, after film formingtreatment on a substrate by means of a plasma CVD apparatus.
 12. Theprocess of plasma cleaning for CVD chambers according to claim 11wherein the concentration of the fluorine gas capable of generatingplasma by electric discharge is more than 20% by volume to less than100% by volume and the concentration of the gas substantially incapableof reacting with fluorine in plasma is more than 0% by volume to notmore than 80% by volume provided that the total concentration of thefluorine gas capable of generating plasma by electric discharge and thegas substantially incapable of reacting with fluorine is 100% by volume.13. The process of plasma cleaning for CVD chambers according to claim11 or 12 wherein the pressure in the chamber is from 50 Pa to 1000 Pa,and the flow rate of fluorine gas is from 50 sccm to 1000 sccm in thecleaning.
 14. The process of plasma cleaning for CVD chambers accordingto any one of claims 11 to 13 wherein the plasma generation fromfluorine gas is conducted by electric discharge in a process chamber ofthe plasma CVD apparatus whereinto the fluorine gas has been introduced.